In this work, we demonstrate non-reciprocal light transport in a quantum system of hot atoms, where the non-reciprocity and quantum correlations derive from reservoir engineering and spin wave interference. Building upon the non-Hermitian platform we developed earlier [1]}, [2]}, our setup consists of an array of optical channels immersed in an ensemble of hot atoms, with dissipative, inter-channel couplings mediated by atoms outside the regions illuminated by the lasers. We identify the unilluminated region as a non-Markovian reservoir, whose memory is determined by the lifetime of the ground-state atomic spins. In contrast to previous studies [3]}, [4]}, [5]} of non-reciprocal transport under electromagnetically induced transparency (EIT) where the Doppler-broadening of the EIT linewidth plays a key role, we investigate light transport between two spatially separated optical channels, where the Doppler effect is irrelevant to the observed transport properties.
Furthermore, the phase of the spin excitations as well as parameters of the third, ancillary optical channel are all tunable, thus providing ample tools for reservoir-engineering. A prominent feature of the current configuration is the sensitive dependence of inter-channel light transport on the optical phases, which significantly impact the dissipative coupling between the optical channels and spin excitations in the reservoir. Subsequent manipulation of optical phases, particularly that in the ancillary channel, enables non-reciprocal light transport. We further identify quantum correlations between the two transport channels, which only exist in the presence of the ancillary channel in the reservoir. The observed quantum correlations here derive from the engineered reservoir, fundamentally different from previous works [1]}, [2]} where quantum correlations were established via inter-channel couplings mediated by an unstructured environment.
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